It is often desirable for a user to be aware his/her bodily function measurements. Recently, many individuals wear small portable devices capable of measuring their heart rate (HR) and other physiological information. One of the techniques used by these devices to measure heart rate is photoplethysmography (PPG). Many of the small portable fitness devices are wearable electronics that are typically package in the form of a watch (e.g., smart watch), activity monitoring band (e.g., worn on the wrist), etc.
However, these devices typically have one or two light sources that illuminate light into the user's skin and one or two detectors to measure the reflected light in order to obtain the PPG measurement. In the everyday course of the user's activities, however, these wrist-worn devices are susceptible to rotation around the wrist (e.g., when a user is walking, etc.) Even a small rotation of the device around the user's wrist can cause decrease in accuracy by a factor of two. This is due to the amount of measured light because the arteries in the portion where a user typically wears a wrist-worn device are rather sparse. Thus, these wrist-worn devices may not always be able to obtain the most accurate PPG measurement due to having only a small number of light sources and detectors which may not always be located at the optimum location around the user's wrist due to rotations of the device around the user's wrist during the course of their everyday life.